thrust bearings<\/a>. A pair of mating helical gears consists of one left-hand twist and one right-hand twist gear, unlike spur gears where the teeth are always parallel with the axis.<\/p>\nDouble Helical Gear<\/h3>\n
Double helical gears are a special type of helical gear. They were created to overcome the high axial thrust associated with single helical gears.<\/p>\n
Double helical gears combine two opposite orientations of teeth together, usually along the middle of the gear face. The axial thrust produced by the left-hand tooth is nullified by the right-hand tooth, thus eliminating the need for a thrust bearing.<\/p>\n
Typical use-cases for double helical gears include prime movers such as gas turbines and generators. They also find use in fans, pumps, and compressors.<\/p>\n
As in the case of single helical gears, double helical gears also provide smooth and silent operation at all speeds<\/strong>.<\/p>\nHerringbone Gear<\/h3>\n
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Herringbone gear is a special type of double helical gear. Whereas the helical gear has a groove in the middle between the teeth, the herringbone gear does not.<\/p>\n
Such a design helps to cancel out the axial forces on each set of teeth. Thus, larger angles are allowed as there is less danger of failure.<\/p>\n
It normally uses the intersecting axes configuration where the two shafts are perpendicular to each other. The power is transmitted from the herringbone gear to a regular double helical gear.<\/p>\n
Herringbone gear does not produce any axial thrust<\/strong> and ensures a quieter, smoother, and effective operation at all speeds and loads<\/strong>.<\/p>\nScrew Gear<\/h3>\n
Screw gear is also known as crossed helical gear. They are used for motion transmission between non-parallel non-intersecting shafts.<\/p>\n
While helical gears usually engage between parallel shafts, screw gears do so at 90 degrees.<\/p>\n
The teeth on a screw gear are in the form of a helix. They form a point of contact between two gears and hence are not very suitable for high load and high-speed applications<\/strong>. They also have low efficiency<\/strong> compared to other helical gears.<\/p>\nA unique trait of screw gears is that they use the same hand pair when engaging. Motion is transmitted as the same hand pairs slide against each other. Lubrication of screw gears is therefore a necessity. There are no limitations on the combination of the number of teeth.<\/p>\n
Bevel Gear<\/h3>\n
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The types of gear we call bevel are cone-shaped, placing the teeth on the conical surface. The cone top is lopped off. The two mating gears are generally placed on perpendicular intersecting shaft axes.<\/p>\n
One of the most common uses for bevel gears is for changing the power transmission axis<\/strong>. While doing so, RPM and torque may be changed as necessary by varying the gear size.<\/p>\nThere is also the option to increase or decrease the angle between the shafts. The two shafts need not be exactly perpendicular.<\/p>\n
Due to the design of bevel gear, when two mating teeth come in contact, the contact takes place all at once instead of gradually. Thus, a similar problem of high stress as in the case of spur gears occurs.<\/p>\n
This high impact mating produces more noise and causes excessive stress on the gear tooth<\/strong>. The high stress ultimately affects the durability and service life of the bevel gear.<\/p>\nIt also affects the sort of applications they are used for. Straight bevel gears are generally used at low RPM (less than 500 RPM or 2 m\/s circumferential speed).<\/p>\n
Despite these limitations, they find use in many different industries. Some of the equipment that uses bevel gears are automobiles, pumps, machine tools (milling and turning<\/a>), food packaging equipment, fluid control valves, and gardening equipment. They are also the easiest to manufacture and hence, are quite affordable and available in a variety of sizes.<\/p>\nSpiral Bevel Gear<\/h3>\n
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Spiral bevel gears are used to overcome the limitations of straight bevel gears. As the name suggests, the teeth on a spiral bevel gear are arranged in the form of a spiral.<\/p>\n
When two spiral gears come in contact, they do so gradually. This avoids impact loading of the teeth as the previous gear teeth pair (that are now losing contact) are still carrying some of the load. From this pair, the new mating pair assumes the load slowly.<\/p>\n
This makes the operation smooth and quiet<\/strong>. It also increases the safe loading capacity of the gear. Thus, spiral bevel gears find use in highly demanding applications<\/strong> (speeds greater than 500 RPM) for safe and reliable operation.<\/p>\nSome of these applications are power transmission, car differentials, robotics, bow and stern thrusters in ships.<\/p>\n
Mitre Gear<\/h3>\n
Mitre gears are bevel gears with a speed ratio of 1:1. An engaging pair will always have the same number of teeth. They transmit power between intersecting axes.<\/p>\n
Mitre gears are used in machines to change the direction of rotation only<\/strong>. They do not cause a change in the shaft speed or torque.<\/p>\nA mitre gear may be of straight or spiral type. Straight mitre gears offer the advantage of not having to deal with any axial thrust. But they come with the limitations of straight bevel gears. Spiral mitre gears produce axial thrust necessitating the need for thrust bearings.<\/p>\n
Mitre gears usually engage at 90 degrees. But they may be produced to mate at other angles as well. If they mate at any other angle between 0 and 180, they are known as angular mitre gears. Most common range for angular mitre gears is between 45 and 120 degrees.<\/p>\n
Hypoid Gear<\/h3>\n